Monitoring the functioning of a cylinder cut-off in internal combustion engines having multiple cylinders

ABSTRACT

A method is described for monitoring the temporary cut-off function of the gas exchange valves of individual cylinders or cylinder groups in internal combustion engines, in which the gas exchange valves of the cylinders to be temporarily cut off are deactivated in the closed state for the duration of the cutoff. Two signals, which supply a measure for the air mass flowing into the internal combustion engine, are compared for monitoring purposes. A disproportion between both signals is interpreted as a fault in the described chain of action.

FIELD OF THE INVENTION

The present invention relates to monitoring the cut-off function ofindividual cylinders or cylinder groups in internal combustion engineshaving multiple cylinders.

BACKGROUND INFORMATION

In multi-cylinder internal combustion engines, individual cylinders orcylinder groups are conventionally cut off during partial engineoperation, in other words, switched between full engine operation usingall cylinders, and partial engine operation using only a part of thecylinders, such as only one cylinder group of a V-engine. As a result ofthe cut-off, the remaining cylinders which are still operating inpartial engine operation are operated with increased cylinder chargewhen compared to full engine operation, and thus at improved efficiency,resulting in better fuel consumption.

The cut-off may be implemented, for instance, by deactivating the gasexchange valves, e.g., those valves controlling the change of thecylinder charge. For example, the intake valve as well as the exhaustvalve of the particular cylinder are closed for the duration of thedeactivation to effect the cut-off.

In this context, a particular problem may arise that in those caseswhere full engine operation is desired, the gas exchange valves of oneor more cylinders are incorrectly deactivated. Likewise, the oppositeerror may occur; the gas exchange valves of one or more of the cylindersto be cut off are not properly deactivated when partial engine operationis desired.

SUMMARY

An example embodiment of the present invention makes it possible tomonitor whether the valves of the cylinders capable of being shut offare properly activated during full engine operation, and whether, inpartial engine operation, the valves of the cylinders to be shut off areproperly deactivated.

This allows, for instance, in the case of undesirably deactivated gasexchange valves, to additionally cut off the fuel injection of therespective cylinders, so that an over-enrichment of the fuel/air mixturefor the remaining cylinders may be prevented.

If no counter-measures were taken when the gas exchange valves areundesirably activated, the fuel injection of the cylinders to be cut offwould be properly switched off. The undesirably active gas exchangevalves cause an undesired rate of airflow through the cylinders to becut off, which is effectively missing in the properly functioningcylinders. Since the control device calculates the fuel quantity for theproperly functioning cylinders as if they were to process the entire airquantity, these cylinders are metered too much fuel, which results indeterioration in the emission behavior and in the performance of theinternal combustion engine. Here, too, the amount of fuel metered to theproperly working cylinders may be corrected as a counter measure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the technical field of the present invention.

FIG. 2 shows a flow chart as an exemplary embodiment of the method ofthe present invention.

DETAILED DESCRIPTION

In FIG. 1, “1” represents an internal combustion engine having acombustion chamber 2, fuel injector 3, intake valve 4, intake valveactuator 5, exhaust valve 6, exhaust valve actuator 7, intake manifold8, throttle valve 9, sensor 10 for throttle valve angle alpha, air massflow meter 11, intake manifold pressure sensor 12, engine temperaturesensor 13, speed sensor 14 and lambda sensor 15 in exhaust pipe 16, aswell as an electronic control device 17.

The electronic control device processes the signals shown concerningintake-air mass ML, throttle valve opening angle α, intake manifoldpressure p, engine temperature tmot, rotational speed n and fuel/airmixture composition lambda, to form control signals for the internalcombustion engine, for instance, to form fuel injection pulse widths ti,ignition signals etc. In FIG. 1, the control device also generatessignals EVS and AVS, which determine the activation and deactivation ofgas exchange valves 4 and 6, and thereby the cylinder cut-off. Thespecific implementation of the valve actuation, whether hydraulic,mechanical, or controllable either individually or as a group, is notdecisive. In any case, however, the control device can activate anddeactivate the intake and exhaust valves.

FIG. 2 shows an exemplary embodiment of the method of the presentinvention. After the diagnostic program is launched, in step 3.1, afirst signal NLS for the air mass flowing into the internal combustionengine is formed from throttle opening angle a and signals EVS, AVSabout the activation of the gas exchange valves.

In step 3.2, a second signal HLS for the air mass flowing into theinternal combustion engine is formed from intake-air mass ML. Thesequence for forming of NLS and HLS may also be reversed. In step 3.3,the amount of the difference is calculated from the first and second airmass signals and its absolute value is compared with a threshold valueS. If, for example, the difference amount is smaller than the thresholdvalue, the cylinder cut-off function is deemed operative (step 3.4). Ifthe amount is greater than the threshold value, an error message isgenerated in step 3.5.

Instead of using the difference, it is also possible to compare aquotient, derived from signals HLS and NLS, to a predefined referencevalue. If the quotient is approximately 1, the cylinder cut-off functionis operative.

A significant deviation from value 1 signals a malfunction in theactivation or deactivation of the cylinders. The extent of thedeviation, which allows differentiation between an operative and amalfunctioning cylinder cut-off function, can be determined by benchtesting and stored in electronic control device 17 for later use duringthe operation of the internal combustion engine.

The generation of the first air mass signal is based on the assumptionthat the cylinder cut-off function is operative. If the cylinder cut-offfunction is indeed operative, the first air mass signal derived fromthrottle opening angle alpha and control signals EVS, AVS, will thenalso correctly reflect the actual cylinder charge. It is also possibleto take intake-manifold pressure p into consideration in forming thefirst air mass signal, either alternatively or in addition to throttlevalve angle alpha. Engine speed n may also be considered in forming thefirst air mass signal, but only additionally, not alternatively. Theactual cylinder charge is also reflected in second air mass signal HLS,irrespective of which control signals EVS, AVS are used in theelectronic control device. In other words: optimally, if the valvecontrol is operative, the first and second air mass signals do notdiffer, which, via step 3.3, leads to the result of step 3.4.

According to the present embodiment of the present invention, formonitoring purposes, two signals which supply a measure of the air massflowing into the internal combustion engine are thus compared.

The second signal is provided by an air mass flow sensor, such as ahot-wire or hot-film air mass flow sensor. This signal represents theair actually flowing into the internal combustion engine, be it duringfull engine operation or during partial engine operation.

The first signal, for instance, is formed by taking into account theintake manifold pressure, the rotational speed and the number of thedesirably active cylinders. At a given speed and pressure, for example,the air mass flowing into the engine will be greater during full engineoperation than in partial engine operation.

In the above-described fault situations, a disproportion exists betweenthe air mass signal calculated from the signal of the air mass meter andthe air mass signal calculated from the intake-manifold pressure. Todetect the disproportion, the quotient of both signals is low-passfiltered in each engine operating mode and compared with a threshold.The respective fault is set if this threshold is exceeded or undershot.For instance, if the air mass calculated from the intake-manifoldpressure constitutes the numerator and the measured air mass thedenominator, and if some cylinders are undesirably deactivated, thequotient will be greater than expected. In contrast, if some of thecylinders to be cut off are undesirably active, the quotient will besmaller than expected.

In one exemplary embodiment of the present invention, a fault might beinferred if, during desired full engine operation, the quotient isgreater than expected, the fault being verified through an analysis ofthe irregular running of the internal combustion engine. The analysis ofthe irregular running can be carried out by evaluating the fluctuationsin the angular velocity of the crankshaft, and may also be additionallyused to identify the affected cylinder. The undesired deactivation ofthe gas exchange valves of the affected cylinder during desired fullengine operation causes a loss of the torque contribution of thiscylinder, which occurs periodically and which periodically brakes, orfails to accelerate, the crankshaft. The position of the missingacceleration relative to a reference angle of the crankshaft, such asthe dead center of the piston of the first cylinder during the powerstroke, makes it possible to identify the affected cylinder and thusallows a controlled cut-off of the fuel supply to this cylinder. Inmodern motor vehicles, an evaluation of the irregular running is alreadybeing carried in order to comply with legal requirements relating toon-board diagnosis of faults relevant to the exhaust gas system, such ascombustion misses in the operation of the internal combustion enginesused as automotive propulsion.

What is claimed is:
 1. A method for monitoring a temporary cut-offfunction of gas exchange valves of an individual cylinder or cylindersgroup in an internal combustion engine, gas exchange valves of cylindersto be temporarily cut off being deactivated in a closed state for aduration of the cut-off, the method comprising: comparing two signalswhich provide a measure for an air mass flowing into the internalcombustion engine; and determining a malfunction of the temporarycut-off function if a disproportion is detected between the two signals;wherein a first one of the two signals is provided by an air mass meter,and a second one of the two signals is formed as a function of an intakemanifold pressure, a speed, and a number of cylinders desired to beactive.
 2. The method according to claim 1, wherein the air mass meteris a hot-wire or hot-film air mass meter.
 3. The method according toclaim 1, further comprising: detecting a disproportion by low-passfiltering a quotient between the two signals in each engine operatingmode and comparing the quotient to a threshold.